Several lines of research have shown that the psychostimulants amphetamine and cocaine act by dramatically increasing dopamine release from dopamine neuron terminals in the nucleus accumbens. Dopamine release increases with repeated drug exposure in a process known as sensitization that is thought to underlie addiction. The candidate proposes to examine this synaptic substrate for psychostimulant action, characterizing the function of individual dopamine neuron synapses and their plastic capabilities. Career development will be fostered by the implementation of molecular and imaging techniques essential to this program of research. The specific aims are as follows: Aim 1. To elucidate the impact of glutamate as a cotransmitter in dopamine neurons. Recent findings from this laboratory suggest that glutamate is a co-transmitter in dopamine neurons. Using micro-cocultures of dopamine and accumbens neurons, the functional interactions between dopamine and glutamate will be studied using whole cell patch recording. These studies will be extended to the brain slice to examine corelease using cyclic voltammetry and patch recording. Transgenic techniques will be used to manipulate glutaminase, the enzyme that produces neurotransmitter glutamate, to reveal the consequences of removing glutamate from dopamine neurons. Aim 2. To characterize dopamine action on accumbens GABA synapses. GABA synapses intrinsic to the accumbens are a principal site for dopamine action. These will be examined with coordinated electrophysiological and imaging techniques focusing on the action of dopamine at individual synaptic sites and possible synaptic heterogeneity. Aim 3. To examine how psychostimulants and nicotine modulate DA synapses. Differential release of dopamine and glutamate from dopamine neuron synapses may be fundamental to the development of sensitization. This will be addressed in micro-cocultures using electrophysiological and Ca2+ imaging techniques to elucidate the relative actions of the psychostimulants and nicotine on dopamine and glutamate release. Activity-dependent and drug-induced plasticity of dopamine neuron synapses will be examined as a cellular substrate for sensitization. The results of these studies should provide the impetus for the development of new pharmacological interventions targeted at reversing sensitization and thus addiction.